This invention relates to a photographic printer, and more particularly to a photographic printer which allows anyone without skill to correct the exposure of images and determine the optimal exposure for printing.
The exposure for printing a color film is generally determined by the LATD (large area transmittance density). With the LATD method, however, the yield of producing satisfactory printing is about 70%. It is therefore necessary for an operator to visually inspect a film negative prior to the LATD measurement (either at a preliminary inspection apparatus or at an exposure opening of the printer before exposure), and determine an amount necessary to correct the LATD-measured exposure (usually with a density key, color key, function key, color correction key, etc.) judging from the relationship between the main objects and background or from patterns thereof he/she empirically learned so that both amounts may be summed up so as to perform printing with an optimal exposure. FIG. 1 shows an example of the relationship between correction keys and corresponding exposure amounts. This conventional method, however, suffers detriments as the operators require much experience and several years of skill, and the quality of printing consequently fluctuates depending on the operators or working conditions. Even if an operator has accumulated enough skill after long training, he/she may retire or leave the shop, giving another difficulty to the management. A better method has been sought in the field.
Using the conventional method and sampling a large number of operators, both skilled and unskilled, a survey was conducted to measure deviations from the preset optimal correction caused by skilled operators and by unskilled operators. The result reveals that the deviation widely fluctuates even among skilled operators depending on image patterns or on individuals. As shown in FIG. 2, about 98% of the judgements made by skilled operators are distributed in the range of .+-.50% from the optimal correction amount (0%) while that of the unskilled operators with 4 month's experience range .+-.70%. In FIG. 2, the curve I denotes the amount of exposure skilled operators judged necessary to correct LATD determined exposure and the curve II that judged by unskilled operators. The graph shows that, although both skilled and unskilled operators judged insufficient amount as the optimal value of correction, unskilled operators tend to judge more insufficient values as the optimal, resulting in defective printing quality. As the conventional method largely depends on individual experience and craftsmanship, only large-scale developing laboratories which can retain a large number of skilled operators can produce prints of high quality.
In order to solve these problems, there has been proposed an automatic exposure determining method comprising the steps of dividing a film frame into small picture elements, and photographically scanning them, and analyzing the thus obtained density values, and combining the analyzed values with data and determining the exposure. But the method is not quite satisfactory as the quality still fluctuates if the exposure is corrected fully automatically. Another method has been proposed to use human judgement by an operator in one way or another as an input to improve the above methods. For example, Japanese Laid-open Patent No. 150336/1976 proposed a method wherein density failure or over- or under-exposure is determined visually and the information is recorded or memorized by an operator and then the exposure is determined in the system by obtaining the minimum density of a shadowed portion if the classified data shows that the average density is high and by obtaining the maximum density of a highlight portion if it shows that the average density is low. In other words, density failure is visually specified so that when the average density is high, the main object is judged to lie in the shadowed portion, and the exposure is judged from the minimum density. However, even if the average density is high, the main object does not necessarily exist in the shadowed portion. When the exposure is determined from the minimum density even if the main object lies in the shadowed portion, it would sometimes be a grave mistake because the minimum density often becomes equal to the fog density of images, and is irrelevant to the main object. In the inspection apparatus disclosed in Japanese Laid-open Patent No. 62428/1977, the position of images is rotated by 90.degree. or 180.degree. to a normal position with a visual determination made by means of switching circuit with a push-button. But this method can merely correct the position of images but cannot obtain correction amounts with respect to the main object.
There have been known (in Japanese Laid-open Patent No. 98821/1973 and No. 62429/1977) methods wherein correction amount is estimated by a visual inspection based upon scanning data to modify the result of an automatic judgement. But such a method requires two operations both in judgement for the necessity of correction and in judgement for the amount, besides skill to achieve a high acceptance rate and processing ability. Moreover, it is extremely difficult to estimate the result of a complex operation in automatic judgement. In order to improve the method to judge the correction amount, it is easily contrived that the data of a scene type (e.g. whether it is taken with strobe, it is open scene, or a show scene) is visually determined for the scenes which are particularly difficult to be judged automatically and the result of automatic judgement is corrected with an amount which has been predetermined for each scene type. Although a film negative with strobe tends generally to be judged to be of insufficient density, some of them have normal or excessive density and they may be over-corrected. Moreover, the scene type data is inconvenient in that definition of scenes is solely dependent on an individual judgement and that a large number of scenes have to be assumed in advance. A strobe scene against white walls in a background may be as different from the one against furniture in a background as to be of an entirely different category. The same is applicable to the relationship between the one against a pitch-dark background and a close-up. The relationship of a main object against a background may widely vary and therefore, the necessary exposure or correction thereof may correspondingly vary by a wide margin.
The conventional automatic judgement methods with an input of a visual inspection result can achieve only limited effect as it is so constructed that an exposure is first judged by an automatic judgement section and when a difficulty is expected, a preset correction amount is supplementary inputted in order to correct the result of the automatic judgement. Furthermore, as the visual judgement data is on the patterns in a film negative and includes no or almost no density data on the main object, the effect of the data is quite limited and can achieve only limited improvement in the acceptance rate. As described above, the level of the automatic judgement method or the automatic judgement method combined with supplemental visual judgement data has not yet reached the stage where prints of a high quality can be produced at a lower cost in a shorter time. At small developing shops, on the other hand, they may need a method which can process films of a high quality and high acceptance rate uniformly by unskilled or inexperienced operators even if it may take a longer time. Therefore, a new photographic printing system which allows cooperation between man and machine has long been sought.
A method which can achieve a high acceptance rate without requiring the skill of operators and apparatus to display film images on a monitor TV and correct exposing conditions have been disclosed (e.g. Japanese Laid-open Patent Application No. 101643/1984, No. 62243/1981 and No. 83733/1981). In all of those methods, images displayed on a monitor TV are corrected to the optimal images manually in a trial-and-error manner to calculate correction in exposing conditions. Since the tolerance range with respect to the correction is wide and since the optimal image conditions on the monitor TV do not always coincide with the optimal printing conditions, the methods still require skill and experience to make the optimal correction. They also are defective in that they need an expensive high-quality display unit as they have to display high-quality images. These methods therefore are put into practice exclusively for professional photographers who earn a higher profit per print sheet and who could thus afford trial-prints.